1. Field of the Invention
The present invention relates to integrated circuit (IC) manufacture and more particularly to an apparatus and method for improving electromigration reliability of dual damascene interconnects through the introduction of material reservoirs in the form of dummy via plugs.
2. Description of Related Art
Modern integrated circuits use electrically conductive interconnections to connect the individual devices on a chip or to send and receive signals external to the chip. Common types of interconnections include aluminum (Al) alloy interconnection lines and copper (Cu) interconnection lines coupled to individual devices, including other interconnection lines, by interconnections through vias. In order to enhance interconnect speed and reliability, the semiconductor manufacture industry is moving away from blanket deposition and etch of Al-based metallizations towards single damascene and dual damascene interconnect structures with Cu-based metallizations.
A major reliability concern in today's integrated circuits is failure of metallic interconnects mainly due to electromigration. Typically, an interconnect system is connected through via plugs to other metal layers or to silicon. Studies have shown that via plugs are places of atomic flux divergence, making them a primary electromigration reliability concern. Electromigration imposes limits on the maximum allowed currents in interconnects. Electromigration is electric current-induced metal self-diffusion, where in places in which atoms are depleting a more tensile stress develops, while in places where atoms are accumulating a more compressive stress develops. If tensile stresses become too large, voiding occurs. Subsequent metal void growth under continued electromigration during normal microprocessor operation would generally lead to interconnect failure. Similarly, if compressive stresses become too large, metallic extrusions can form which can lead to short circuit of the integrated circuit (IC) device.